1. Academic Validation
  2. Phosphorylation of RAB7 by TBK1/IKKε Regulates Innate Immune Signaling in Triple-Negative Breast Cancer

Phosphorylation of RAB7 by TBK1/IKKε Regulates Innate Immune Signaling in Triple-Negative Breast Cancer

  • Cancer Res. 2020 Jan 1;80(1):44-56. doi: 10.1158/0008-5472.CAN-19-1310.
Jessica L Ritter 1 Zehua Zhu 2 Tran C Thai 2 Navin R Mahadevan 2 3 Philipp Mertins 4 5 Erik H Knelson 2 Brandon P Piel 2 Saemi Han 2 Jacob D Jaffe 4 Steven A Carr 4 David A Barbie 2 Thanh U Barbie 6 7
Affiliations

Affiliations

  • 1 Breast Oncology Program, Dana-Farber/Brigham and Women's Cancer Center, Boston, MA.
  • 2 Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA.
  • 3 Department of Pathology, Brigham and Women's Hospital, Boston, MA.
  • 4 Broad Institute of Harvard and MIT, Cambridge, MA.
  • 5 Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
  • 6 Breast Oncology Program, Dana-Farber/Brigham and Women's Cancer Center, Boston, MA. tbarbie@bwh.harvard.edu.
  • 7 Division of Breast Surgery, Department of Surgery, Brigham and Women's Hospital, Boston, MA.
Abstract

Triple-negative breast Cancer (TNBC) is a heterogeneous disease enriched for mutations in PTEN and dysregulation of innate immune signaling. Here, we demonstrate that Rab7, a recently identified substrate of PTEN Phosphatase activity, is also a substrate of the innate immune signaling kinases TANK-binding kinase 1 (TBK1)/IκB kinase ε (IKKε) on the same serine-72 (S72) site. An unbiased search for novel TBK1/IKKε substrates using stable isotope labeling with Amino acids in Cell Culture phosphoproteomic analysis identified Rab7-S72 as a top hit. PTEN-null TNBC cells expressing a phosphomimetic version of Rab7-S72 exhibited diffuse cytosolic Rab7 localization and enhanced innate immune signaling, in contrast to a kinase-resistant version, which localized to active puncta that promote lysosomal-mediated stimulator of interferon genes (STING) degradation. Thus, convergence of PTEN loss and TBK1/IKKε activation on Rab7-S72 phosphorylation limited STING turnover and increased downstream production of IRF3 targets including CXCL10, CCL5, and IFNβ. Consistent with this data, PTEN-null TNBC tumors expressed higher levels of STING, and PTEN-null TNBC cell lines were hyperresponsive to STING agonists. Together, these findings begin to uncover how innate immune signaling is dysregulated downstream of TBK1/IKKε in a subset of TNBCs and reveals previously unrecognized cross-talk with STING recycling that may have implications for STING agonism in the clinic. SIGNIFICANCE: These findings identify Rab7 as a substrate for TBK1 for regulation of innate immune signaling, thereby providing important insight for strategies aimed at manipulating the immune response to enhance therapeutic efficacy in TNBC.

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